FIG. 10 shows an example of conventional heater. The heater X illustrated in the figure includes a substrate 91, a heating resistor 92, an electrode 93 and a protective film 94. The substrate 91 is in the form of an elongated rectangle and made of an insulating material. The heating resistor 92 is made of e.g. Ag—Pd and formed in the form of a strip on the substrate 91. The electrode 93 is for supplying electrical power to the heating resistor 92 and mainly made of Ag. The protective film 94 is made of e.g. glass and covers the heating resistor 92 and part of the electrode 93. The heater X is used for thermally fixing toner to recording paper. When electrical power is applied from a power supply to the heating resistor 92, the heating resistor 92 generates heat. Recording paper to which toner has been transferred is pressed against the heater X in the heated state using a platen roller. As a result, toner is fixed to the recording paper.
The heater X has a drawback that the separation of the heating resistor 92 and the electrode 93 may occur. The separation can be caused by generation of bubbles or deterioration of the bonding strength due to the diffusion of Ag contained in the electrode 93. The separation generally tends to occur at the portion where the heating resistor 92 and the electrode 93 overlap each other. When the separation occurs in the manufacturing process, the heater X is disposed of as a defective product. When the bonding between the heating resistor 92 and the electrode 93 is deteriorated during the use, the heating resistor 92 is not heated sufficiently, which hinders proper printing.
Patent Document 1: JP-A-2004-6289